Subtle eye movements betray the impulsive and impatient

Kevin P. Casey

Eat it now or wait for something better? Like the old marshmallow experiment, a new study sought to tease out who could delay gratification - and who could not - by measuring the movement of their eyes.

Eat it now or wait for something better? Like the old marshmallow experiment, a new study sought to tease out who could delay gratification - and who could not - by measuring the movement of their eyes. (Kevin P. Casey)

Ever notice how a fast-talking short person walking alongside a lanky, laconic friend will eventually leave him in the dust? Despite the difference in the length of the walking partners' legs, the impatient one will get to his destination first every time. Why? Because he just moves faster.

A new study bears out such observations, finding that in the impatient and impulsive, even the tiny, sweeping eye movements we make to scan across our field of vision are more jittery than they are in patient people willing to wait for a reward.

Think of it as an optical version of the famous marshmallow experiment - in which toddlers' ability to delay gratification was measured by their ability to hold off eating a treat, and thereby get a reward, until the researcher, who departed the room, came back. In follow-up studies, those children who were unable to delay gratification in order to earn an extra reward were found more likely, as adults, to be overweight or obese, to have been divorced, to have had brushes with the law, and to have abused drugs or alcohol.

In short, impatience - and the restless speed of action that appears to come with it - may win footraces. But it may be a slightly less adaptive trait in modern society, and a good measure for it might be a highly useful thing to have.

The marshmallow study also may have suggested that children with low impulse control were somehow morally weak human beings. The current findings - that impatience is so fundamental a trait that it shows up in the involuntary movement of our eyes - suggests a far kinder conclusion: that while patience can perhaps be practiced and learned, impulsiveness - and its consequences - are not wholly under our control.

In this study, published Tuesday in the Journal of Neuroscience, researchers from Johns Hopkins University had subjects sit with their heads immobilized in front of a screen and track a shifting dot. As they did so, they measured the "vigor" of their eyes' saccades - both the speed and the sweep of their eye movements as they took in the visual field before them.

On another day, the subjects were brought in and seated in front of a screen and given instructions to track a dot that shifted to different positions across the screen. Only on this day, the researchers weren't measuring the vigor of the subjects' saccades, but their impatience.

A subject's impulsiveness - his or her ability to delay gratification in exchange for a slightly increased reward - was measured another way too: by a standard psychological questionnaire that asked the subject to rate, say, how often he or she bought something on impulse or spoke before thinking things out.

But in front of the screen, impulsiveness was measured by how much time it took for the subject, during an eye-tracking task, to follow a new command that required her to suppress the urge to follow a previously established pattern. Like the Stroup test used widely in neuro-psychological testing, this exercise measures one's ability to inhibit an automatic response in order to complete the task as directed. Those who took longer to track the dot when the instructors' command changed had to work harder to resist their impulse; that identified them as more impulsive and impatient than those who could follow the change of command without delay.

The researchers here altered the exercise to better gauge subjects' ability to delay gratification. Subjects were told that they could increase their performance score - and with it, reap a small financial reward - by waiting for an additional command before shifting their gaze to the new target on the screen. Some subjects optimized their payout by demonstrating a willingness to wait for a new command. Others were too impatient, and did not.

By these complex measures of "temporal discounting," the ability to wait for a higher reward was indeed correlated with the vigor of the subjects' saccades. But the same statistically significant relationship was not found between eye-movement vigor and the questionnaire-based measures of impulsiveness. The trend was the same - that more impulsive people showed more vigorous eye movements.

But it was weak, suggesting that self-evaluating questionnaires may not be capturing fundamental inclinations toward impulsiveness, or may reflect learned behaviors or socially acceptable preferences rather than the true level of impatience that may drive a person.

The latest study was conducted by researchers at Johns Hopkins University's departments of biomedical engineering and neuroscience, led by bionengineer Jennie E.S. Choi.